The decoration of foods with food colorings is common practice to enhance the visual aesthetics of comestibles. The complexity and intricacy of such decorations has increased recently with the introduction of ink jet systems to foods. One example is the use of such systems for decoration of bakery items like cakes, wherein a consumer can have a picture of her choice imprinted on rice paper and put it on the icing of the cake.
Up until recently, the ink jet system has been considered slow for the production of high volume production articles like sheeted dough's and snacks. Russell et al., Mar. 18, 2004, Printing Process With Edible Inks, U.S. 2004/0050289A1, for example, favors a lithographic printing for high volume food articles. Others have also used rotary printing devices. For example, in U.S. Pat. No. 5,534,281, issued Jul. 9, 1996, and U.S. Pat. No. 5,162,119, issued Nov. 10, 1992, both to Pappas et al, it is disclosed the use of a rotary printer to print images onto a dough substrate.
These systems, however, are physically limited in the number of images they could print. A rotary printer, for example, has embossed images in the limited surface area of the roll. Once a revolution of the roll has been completed, the same images will be printed again in a subsequent revolution. Since consumers are constantly looking for variety, such systems would be unsatisfactory. These systems also have the disadvantage of direct contact of the printing equipment with the food substrate, which can create sanitation, reliability and quality issues, and create problems when attempting to register multiple colors. Furthermore, challenges are created when printing to fragile substrates or media like fabricated snack chips, cookies, crisps or crackers.
The jetting frequencies at which an inkjet print head can repeatedly jet ink from a nozzle are a function of the specific inkjet technology upon which the print head is based and the ink properties used in such print heads. Drop-on-demand piezoelectric inkjet (DOD-PIJ) is a specific technology that is particularly suitable for the printing of high volume foods, however, its jetting frequency so far has been limited to a maximum ink jet frequency of about 20 KHz (thousands of drops per second). Also, the profile of droplet characteristics (e.g., velocity, satellite, ligament, size, mass, and shape) as a function of jetting frequency for conventional inks limits the operating window throughout the jetting frequency spectrum that would be encountered upon printing for consistent printing quality and reliable jetting performance of different images. A modification of ink to provide a consistent droplet characteristic would be valuable for improving printing image quality.
Satellite drop formation (i.e., the occurrence of one or more undesirable droplets formed next to or in close proximity to primary drops, each originating from the same ink jet nozzle) has been seen for conventional inks that cause unrecognizable images, severe blurring, poor readability and serious reduction in jetting reliability. Thus, such satellite drop formation is undesirable and must be limited.
Unlike thermal bubble jet ink which uses water as a main component of edible inks, the level of water content in piezoelectric printers is vastly limited due to the considerations of water interaction with electrical field and water weakening of the bonding adhesive used. It would therefore be advantageous to develop inks for use with DOD-PIJ print heads to print on food substrates at high speed with readable text and/or images since such inkjet system is not constrained to a maximum number of different text and/or images by the equipment and since contact of the printing equipment and the food substrate is avoided. It would also be advantageous to develop inks with consistent droplet size and velocity across the spectrum of jetting frequencies up to 150 kHz. Furthermore, it would be advantageous to make these inks compatible with a food process to enable retention of high quality, readable images even after subjecting the printed substrate to further processing like high-temperature baking or frying.